Conventionally it is considered indispensable in manufacturing a casting that, to obtain a good casting by pouring molten metal into a cavity of a mold that is formed when the upper mold and the lower mold are overlapped, by controlling the flow of molten metal and by limiting any impure substance and gas in the product, a passage for the molten metal called a gating system, which has nothing to do with the shape of a casting (see, for example, Non-Patent Publication 1), be provided. However, the gating system often has lowered the yield rate of castings. Moreover, it also requires removing the gating system after crushing the mold. Thus the gating system often worked disadvantageously to the productivity and the cost efficiency of casting.
Therefore, to improve the yield rate for casting, it is proposed to use a casting method wherein it is carried out by using a lower mold, which is a mold formed by various kinds of molding methods, and which has no gating system, but only a cavity required for casting, and an upper mold, which is a mold formed by various kinds of molding methods, and has no cavity for a gating system, but which has a convex portion capable of forming a cavity for casting. In this casting method it is proposed that, after the molten metal required to produce only the casting is poured into the cavity of the lower mold, the convex portion of the upper mold be advanced into the cavity filled with the molten metal so as to form the cavity required to produce the casting, and that then the upper mold overlap the lower mold (a sand-mold press-casting process) (see Patent Publication 1).
This casting method can easily produce a desired casting without fail while keeping a high yield rate of molten metal.
[Non-Patent Publication 1]
Nihon Chuzou Kogakukai (Japan Foundry Engineering Society), Illustrated Foundry Dictionary, 1st Ed., published by Nikkan Kogyo Sinbunsha, Japan, Nov. 30, 1995, page 212, gating system, and
[Patent Publication 1] Patent Application Publication No. JP2005-52871